An economizer is typically utilized between the condenser and the evaporator of a refrigeration system to cool refrigerant liquid below the temperature at which it leaves the condenser in order to improve the operating efficiency of the system. Flash cooling is achieved by the evaporation of part of the refrigerant liquid as it flows from the condenser through nozzles, orifices, or other pressure reducing means into a chamber which is lower in pressure. The flashing refrigerant cools the remaining liquid by absorbing heat as it vaporizes.
Upon separation from the cooled liquid, the refrigerant vapor, or flash gas, is conveyed to the inlet of a compressor stage operating at intermediate pressure. The cooled refrigerant liquid flows from the economizer to an evaporator, where it is vaporized in heat exchange relationship with another fluid, e.g., water, to satisfy a cooling load.
Refrigerant vapor leaving the evaporator is typically compressed in two stages. After the first stage of compression, it is mixed with the flash gas from the economizer and further compressed, and returned to the condenser to repeat the cycle.
Although an economizer can be used with virtually any refrigeration system in which multiple stages of compression are provided, its use is economically justified only if the overall system cost is thereby reduced, or if the resulting energy savings payback exceeds its cost. Multiple economizer stages generally are not used because there are few refrigeration systems designed with more than two compressor stages, and because a second economizer stage of the prior art design typically cannot be cost justified due to the declining rate of return, i.e., two stages of economizing are less than twice as efficient as one, yet are almost twice as expensive when separate vessels are used for each stage.
It has long been recognized in the art that efficient separation of the flash gas from the cooled refrigerant liquid is essential to efficient operation of an economizer. The violent expansion of the refrigerant as it flashes and rushes into the economizer chamber tends to entrain liquid droplets in the vapor. Various means have been developed to separate the liquid from the vapor, including relatively expensive eliminator screen grids. It is also possible to minimize liquid entrainment in the leaving vapor by distributing the entering refrigerant liquid over a large volume and directing it away from the flash gas outlet. However, previous distribution apparatus designed for this purpose have been somewhat complicated and expensive to fabricate.
Taking the above considerations into account, the present invention is designed to reduce the complexity and part count sufficiently to permit a two stage economizer to be built at substantially less cost than two single stage economizers of prior art design. The resulting multi-stage economizer operates over a wide capacity range, and provides improved efficiency in a compact size.
The following U.S. Pat. Nos. describe prior art relevant to the subject invention.
U.S. Pat. No. 2,277,647 discloses the basic economizer design, in which the flow of refrigerant into a flash chamber is controlled by a float valve. The cooled liquid refrigerant runs out the bottom of the flash chamber and into another chamber containing a second float valve controlling its entry into an evaporator. An eliminator screen is used to separate the liquid from the flash gas before it is conveyed to the second stage of a two stage compressor.
A perforate distributor means is shown in U.S. Pat. No. 3,553,974 for effecting more efficient separation of the liquid refrigerant from the vapor as it expands into a flash chamber. A float valve is used to modulate the flow of refrigerant as a function of cooling load, so that the liquid level is always above the entrance to the perforate distributor means.
U.S. Pat. No. 2,164,761 discloses a two stage economizer in which refrigerant liquid is accumulated in vertical chambers to exert a hydrostatic head pressure in response to load, thereby controlling the flow of refrigerant into an evaporator.